The sensing of leads of a component after the leads have been inserted into the holes of a printed circuit board is disclosed in U.S. Pat. No. 4,549,087 entitled "Lead Sensing System for Component Insertion Machine" issued on Oct. 22, 1985. The disclosed system is premised on sensing the presence or absence of inserted leads via a fiber optic sensor arrangement mounted within the cut and clinch mechanism of the component insertion machine.
Placing a lead sensing system into such a confined area imposes considerable restraints on the ability of the system to sense inserted leads. In this regard, the system disclosed in U.S. Pat. No. 4,549,087 includes both light projection as well as light sensing within this confined area. The light sensing portion of the system must receive reflected light from a small portion of the lead upon which light is projected. The light may not be optimally reflected from the lead due to an imperfection in the lead surface or due to a slight angularity in the lead itself which does not properly reflect light.
A lead sensing system which could analyze the entire area underneath the printed circuit board from where the inserted leads extend would be preferable. Unfortunately, this area does not offer a consistent and predicable background to the inserted leads. In this regard, the solder patterns on the underside of the boards produce different backgrounds to the leads. The ambient lighting in this area also will change due to extraneous environmental conditions.